Coated spinneret and process of coating during spinning



United States Patent 3,136,449 CQATED SPINNERET AND PROCESS 6F CGATH IG DURWG SPINNENG Harry .l. Denies, Hopeweii, Christos L. Kapetanahis, Colonial Heights, and Wiiiiam T. Haggerty, J12, Chester, Va, assigucrs to Allied Chemical Corporation, New York, N.Y., a corporation of New York No Drawing. Filed May 28, 1962, Ser. No. 197,900 7 Claims. (Cl. 18-3) This invention relates to treatment of metallic spinnerets used in the melt spinning of organic filament-forming materials. More particularly, the invention relates to process and the resulting article wherein the outer face of the spinneret is coated with a composition which allows prolonged spinning of high quality filaments.

Since the advent of synthetic organic filament-forming materials to be spun from the melt, in particular polyamides such as polycaproamide and polyhexamethylene adipamide, there has been a continuing search for ways to improve the spinneret surfaces so that a long period of spinnin could be achieved without interruption for cleaning the spinnerets. This problem arises because the organic materials spun in the melt will occasionally leave a small deposit of carbonated organic material, etc. at the spinneret orifice, which deposit or impurity tends to block the orifice and to accumulate molten polymer and thus to build up until an imperfect filament is spun. These accumulations may be of a size to deflect the filament being extruded, to slow down the extrusion, or even to hold back the extrusion until a mass of polymer drips from the orifice.

A great variety of materials known for their anti-sticking properties and/or lubricating properties have been tried as coatings in the orifice and/ or on the outer faces of the spinnerets to alleviate the problems above cited. Very few of these materials, however, have been found to be effective to meet the exacting requirements of a melt spinning process. It will be appreciated that melt spinning processes are conducted at relatively elevated temperatures, usually at least about 120 C. and commonly at least 200 C. or higher. Accordingly, a very stable treating material is needed. Moreover, melt spinning commonly involves production of a large number of fine filaments at high spinning speeds so that even small obstructions in an orifice quickly affect adversely a sizeable quantity of product. Moreover, any interruption of the spinning process, as for treating the spinneret, represents lost production and must therefore be minimized. The qualities required besides stability in a coating material thus include proper balance of cohesion and adhesion to the metal of the spinneret, cleansing power on the spinneret, lubricity toward the organic filament-forming material, proper viscosity for quick spreading in a smooth film, etc.

In accordance with our invention, we have found that a highly efiective coating on the outer face of a metallic spinneret used at temperatures of at least 120 C. for melt spinning, consists essentially of tris (para-biphenylyl) phenyl silane. Related silanes can be present as impurities or as intentional additives, e.g., tetrakis(p-biphenylyl)silane; but our tris-(p-biphenylyl)phenyl silane should be in at least 1:1 weight proportion with such other aryl silanes, in accordance with our invention.

In particular the metallic spinneret can be made of steel, e.g., chromium-containing steel which desirably is free of nickel. Such spinneret coated with our silane composition has proved very efiicient in the melt spinning of, in particular, polyamides at temperatures above the melting point of the polyamide and up to about 300 0., especially in the range about 250275 C.

3,l3,449 Patented Apr. 28, 1964 From a practical point of view, it is important that the treatment of the spinneret can be effected with the spin neret at operating temperatures, so that the coating on the outer face thereof can be renewed with minimum interruption of the spinning operation and in a short time. Accordingly, it is desirable to use a coating composition which can quickly be sprayed on the spinneret while filaments are still being extruded therefrom and which can very quickly be formed into the desired coating on the spinneret. A composition in aerosol form is therefore highly desirable. Our silane composition meets this requirement in that it can be put in solution, and aerosoled in solution and has the necessary properties for quick spreading as a melt on the spinneret face.

The example below describes completely a specific embodiment illustrative of our invention and of the best mode contemplated by us for carrying out the invention; but the invention is not to be interpreted as limited to all details of the example.

Example 1 Tris(para-biphenylyl)phenyl silane in a form melting over the range of about 158 C.172 C. was used in this example. The melting point of pure tris-(para-biphenylyl)silane in one crystal form is about C. and in another crystal form is about 172.5 -174 C. (Journal of the American Chemical Society, vol. 77 of 1955, page 6228).

The silane compound was dissolved in tetrahydrofuran at concentration of about 15 %20% by weight and was aerosoled in conventional manner by the cold filling technique. Suitable propellants are mixtures of monofiuortrichloromethane (2 parts by weight) with difluormonochloromethane (1 part by weight). A still better propellant in that it is more compatible with the tris-(p-biphenylyl)phenyl silane solution is disclosed in copending application of Lloyd T. Planner, Serial No. 220,159, filed Aug. 29, 196 2.

The aerosoled 20% solution of tris-(para-biphenylyl) phenyl silane in tetrahydrofuran solvent was tested as a coating on four A.I.S.I. (American Iron and Steel Institute) type 403 nickel-free, chromium-containing steel 136 hole, 0.018 inch orifice diameter spinnerets in a commercial installation where 4,000 (undrawn) denier, 136 filament poly-e-caproamide yarn was being spun from the melt at about 260-265 C. and about 1,250 feet per minute. A one month period was covered in the test. The tested coating composition was used at one pair of the 4 spinning positions for the first 8 days, then at the other pair of spinning positions for the next 8 days; then again at the first positions for 1 week and again at the second positions for the last week of the test.

The number of times that the coating was reapplied was recorded, including a routine reapplication about 4 times a day, and any special reapplications called for by appearance of carbonized matter, by slow holes, or by drips, or by other defective spinning. The total number of reapplications in a typical Week, mostly for carbonization rather than for filament defects, ran less than 150, which is fully satisfactory by commercial standards.

The spraying of the spinneret was done While the filaments were still being extruded. The filaments were temporarily collected by the operator in a heap for disposal and at the same time he wiped the spinneret face once or twice with a brass stick to cleanse the surface; then sprayed with the aerosol; then allowed the filaments once more to descend down the spinning tower. This whole operation of reapplying the coating took less than one minute on the average.

The yarn produced, using our tris-(p-biphenylyl)phen- -19 yl silane coating, spun and handled fully satisfactorily to give on drawing down to 840 denier a high quality yarn.

When, at the conclusion of this test, the spinnerets treated with our composition were dismounted and routinely cleaned they gave no ditficulty in cleaning and no indication that cleaning should have been done sooner.

Thus our composition was found fully satisfactory for commercial spinning of organic materials from the melt.

We have obtained excellent results in tests of melt spinning polycaproamide using mixtures of the tetra-kisand tris-(p-biphenylyl)phenyl silanes containing as high as 1:1 by weight proportions of the tetrakis component, aerosoled as 15% solutions in tetrahydrofuran and sprayed on the spinnerets, generally as above described. We have found, however, that our composition should contain no more than at most 1 part by weight of tetrakis-(p-biphenylyl)silane per part of tris-(p-biphenylyl)phenyl silane. The mixtures of tetrakis and tris compounds from viscous liquid at about 250 C. and above on evaporation of their solutions in, e.g., tetrahydrofuran; but at about the 1:1 proportion, the high-melting tetrakis compound tends to crystallize out of the liquid mixture with tris compound, even at elevated spinning temperatures such as about 26026 C. The resulting solid matter is undesirable.

Crude tris-(p-biphenylyDphenyl silanes usable for our purpose can have melting points as low as about 120 C. These products contain aryl silane impurities such as the above tetrakis compound, the bis-(p-biphenylyl)diphenyl silane, and the like. Such lower melting compositions of our invention are useful in the melt spinning of the lower melting organic filament-forming materials such as polyolefins. For the higher melting materials such as polyamides, polyesters, etc. the preferred compositions of our invention are those which complete their melting in the range between about 150 C. and about 250 C.

The following is an example of use of 1:1 by weight tris-(p-biphenylyl)phenyl silane: tetrakis-(p-biphenylyl) silane mixture in accordance with our invention.

Example 2 A conventional melt spinning apparatus for spinning polyamides was used, employing four identical 32 hole, 0.01 inch orifice diameter type 403 stainless steel spinnerets. Molten linear poly-e-caproamide was fed to the spinnerets at 260 to 265 C. under a pressure of about 3,000 p.s.i. The melt was spun at a minimum rate of 2,400 f.p.m. into 230 denier, 32 filament yarn.

The outer face of each of two spinnerets was sprayed with an aerosol composition containing 15 parts of 1:1 (by weight) mixture of: tetrakis(4-biphenylyl)-silane and tris-(4-biphenylyl)-phenyl silane dissolved in 85 parts of tetrahydrofuran. The aerosol was prepared by the well known cold filling technique using a mixture of about 2 parts of monofluorotrichloromethane and 1 part of difiuoromonochloromethane as the propellant.

The other two spinnerets were sprayed with an aerosol composition containing a polymethylsiloxane oil to serve as controls against which to evaluate the efiiciency of our composition. Upon contact of the aerosol solutions with the hot spinneret face, the solvents evaporated, leaving a coating of molten material. Then the extrusion process was started. Every two hours thereafter the spinneret faces were examined for deflected flicking filaments, carbon deposits, blocked orifices and other evidences of faulty spinneret operation.

The time lapse from the start of the spinning to the time when flicking appeared on the control spinnerets was at most 68 hours. Flicking was not noted on the spinnerets coated with our composition for at least 10 hours. When flicking occurred the particular spinneret was wiped with a brass stick and recoated as described in Example 1.

The filaments spun through the spinnerets coated with the composition of this invention were highly uniform and when drawn showed a reduced number of defects such as broken filaments, as compared with the filaments spun through the control spinnerets.

Our compositions have special utility in the spinning of multifilarnent yarns as above described; and they can also be used on the spinneret face in less demanding spinning operations, e.g., in the extrusion of monofils. For such operations our compositions can be applied by spraying, e.g., in aerosol form as above; or by brushing onto the spinneret face; etc.

We claim:

1. A metallic spinneret bearing on the outer face thereof a coating consisting essentially of tris-(para-biphenylyl) phenyl silane, which coating completes its melting at a temperature in the range between about C. and about 250 C.

2. A spinneret of chromium-containing steel in accordance with claim 1.

3. A metallic spinneret for extrusion of organic polymers bearing on the outer face thereof a coating of tris- (para-biphenylyl)phenyl silane and tetrakis-(para-biphenylyl)silane in weight ratio of at least 1:1.

4. Process of spinning an organic filament-forming material from a melt by extrusion of the melt through a spinneret, which comprises applying to the outer face of the spinneret, while the spinneret is at temperature of at least about 120 C., a coating consisting essentially of tris- (para-biphenylyl phenyl silane.

5. Process of claim 4 wherein a multifilament yarn is spun and the tris-(para-biphenylyDphenyl silane is applied as a solution in aerosol form, by spraying onto the outer face of the spinneret while extrusion of the filaments continues.

6. Process of claim 4 wherein the filament-forming material is a synthetic linear polyamide and the spinneret is of steel.

7. Process of claim 6 wherein the filament-forming material is poly-e-caproamide; multifilament yarn is spun; the spinneret is of nickel-free, chromium containing steel and is at a temperature in the range between about 250 C. and about 275 C.; the tris-(para-biphenylyDphenyl silane composition employed completes its melting in the range between about C. and about 250 C.; and said silane composition is applied as a solution in aerosol form, by spraying onto the outer face of the spinneret while extrusion of filaments continues.

References Cited in the file of this patent UNITED STATES PATENTS 2,719,073 Olson Sept. 27, 1955 

1. A METALLIC SPINNERET BEARING ON THE OUTER FACE THEREOF A COATING CONSISTING ESSENTIALLY OF TRIS-(PARA-BIPHYNYLYL) PHENYL SILANE, WHICH COATING COMPLETES ITS MELTING AT A TEMPERATURE IN THE RANGE BETWEEN ABOUT 120*C. AND ABOUT 250*C. 